The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
Traditionally, magnetic writing has been performed longitudinally on a magnetic disk. A longitudinal write head used in such recording systems includes a coil layer embedded in an insulation layer, the insulation layer being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head and the pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic flux in the pole pieces which causes a magnetic field to fringe out at a write gap at the ABS for the purpose of writing the aforementioned magnetic impressions in tracks longitudinally on the moving media, such as in circular tracks on the aforementioned rotating disk.
In recent read head designs a spin valve sensor, also referred to as a giant magnetoresistive (GMR) sensor, have been employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos Θ, where Θ is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.
The spin valve sensor is located between first and second nonmagnetic electrically insulating read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. In a merged magnetic head, a single ferromagnetic layer functions as the second shield layer of the read head and as the first pole piece layer of the write head. In a piggyback head the second shield layer and the first pole piece layer are separate layers.
The ever increasing demand for increased data rate and data capacity has lead a relentless push to develop completely new recording systems capable of meeting these demands. As a result, researchers have focused on the use of perpendicular magnetic recording systems. Such recording systems operate by recording data as localized magnetizations on a magnetic disk that are oriented perpendicular to the surface of the disk rather than longitudinally. A perpendicular magnetic recording disk includes a magnetically soft underlayer and a thin magnetically hard top layer. It is this top layer that remains magnetized after data has been written. The magnetically soft underlayer acts as a magnetic conduit for conducting magnetic flux back to a return pole.
It turns out however, that magnetic disks suitable for perpendicular magnetic recording are susceptible to stray field writing. As a result, magnetic structures, such as those in the write head must be configured to prevent stray field writing. Structures such as shields and write poles must have a depth as measured from the ABS that is not too deep. This is to prevent the structure from acting as a magnetic antenna which might pick up stray fields and concentrate them at the disk, causing inadvertent writing.
However, this lack of shielding has reduced the magnetic isolation between the writer and read sensor. Magnetic fields from the portion of the write coil that extends beyond the write pole can reach the read sensor and be read as a signal. Field from the writer is picked up by the reader shield, causing the shield's magnetization to flip. This causes an unacceptable amount of signal noise, making the recording system impractical.
Therefore, there is a strong felt need for magnetic head design that can be used in magnetic recording while also preventing interference between the write head and the read sensor. Such a design should also prevent stray field writing to the disk.